Synthesis, Characterization and Polymerization of Ethylene Using a Novel Soluble Magnesium-Titanium Catalyst*
Total Page：16
File Type：pdf, Size：1020Kb
Synthesis, characterization and polymerization of ethylene using a novel soluble magnesium-titanium catalyst* Ganugupati Satyanarayana and Swaminathan Sivaramt Division of Polymer Chemistry, National Chemical Laboratory, Pune 411008, India (Received 4 January 1993; revised 28 May 1993) A l:2 complex of MgCI2 and tetrahydrofuran (THF) was prepared by a simple Grignard decomposition reaction using Mg metal and 1,2-dichloroethane in THF as diluent. The MgC12.2THF complex formed a homogeneous solution with titanium-n-butoxide in xylene at 60°C. The soluble Mg-Ti complex in xylene polymerized ethylene under homogeneous conditions in the presence of organoaluminium compounds. The kinetic behaviour of the polymerization reaction was studied. It was observed that the presence of MgCI2 transformed the Ti centre from a dimerization to a polymerization catalyst. (Keywords: magnesium chloride; titanium-n-butoxide; magnesium-titanium catalyst) INTRODUCTION a Grignard decomposition reaction forms a soluble complex with titanium-n-butoxide, which in conjunction Solid catalysts based on anhydrous MgCI z and Ti halides with organoaluminium compound initiates ethylene have attracted considerable attention during the past polymerization under homogeneous conditions in xylene decade as components of high efficiency ethylene and as the solvent 11. This paper reports our results on the propylene polymerization catalysts 1. The role of MgC12 synthesis, characterization and polymerization of ethylene in these catalysts has been widely discussed in the using this novel soluble Mg-Ti catalyst. literature 2. There are, however, only a few reports of truly soluble Mg-Ti catalysts for olefin polymerization. Soga et al. prepared a soluble metal halide-2-ethylhexanol complex which, in conjunction with titanium-n-butoxide EXPERIMENTAL and diethylaluminium chloride, polymerized propylene 3. Materials This catalyst enabled the authors to study the effect of Magnesium turnings (Loba Chemicals, Bombay, India), the electronegativity of the metal in the metal halide on triisobutylaluminium (TIBAL), diethylaluminium chloride catalyst activity. Yano et al. prepared a MgCI2 2- (DEAC), triethylaluminium (TEAL), trimethylaluminium ethylhexanol complex which, in conjunction with TIC14 (TMA) and trioctylaluminium (TOAL) (all from Schering or titanium-n-butoxide and diethylaluminium chloride, AG, Bergkamen, Germany) were used as received. was used as a catalyst for high temperature polymer- 1,2-Dichloroethane (SD Fine Chemical, Bombay, India) ization of ethylene4'5. In both of these studies, whereas was distilled over Call 2 and stored over 3 A molecular the precursors were hydrocarbon soluble, the true sieves. Polymer grade ethylene was obtained from the catalyst formed by the addition of diethylaluminium Gas Cracker Complex of the Indian Petrochemical chloride was heterogeneous. Corporation Limited (Nagothane, India). It had a More recently, truly soluble Mg-Ti catalysts have been moisture content of <4ppm (Shaw model SHA-TR reported by Makino et al. 6'7 and Zucchini et al. 8 10. moisture analyzer) and oxygen content of <3ppm Reduction of TiCI4 by Grignard reagent or solubilizing (Braun oxygen analyzer). Titanium tetra-n-butoxide anhydrous MgCI 2 with trialkylphosphate was reported (TNB; Synthochem, India) was vacuum distilled twice to result in soluble Mg Ti catalysts capable of co- and was further purified by adding TIBAL (2 ml in 10 ml polymerizing ethylene with propylene6'7. Reaction of of hexane) to TNB (15 ml)dropwise at room temperature. anhydrous MgCI 2 with titanium-n-ethoxide in a 2:1 The colour of the solution turned black. The mixture was stoichiometry results in an isolable bimetallic complex stirred for 30min and distilled at 120°C (0.5mmHg). capable of polymerizing ethylene in a homogeneous Solvents were dried over Call 2 and distilled over Na medium in toluene s lo. wire under a positive pressure of high purity N2 or Ar. We have recently observed that a complex of anhydrous All manipulations involving air-sensitive compounds MgC12 with tetrahydrofuran (THF) prepared in situ from were performed inside a Labconco (model 50004) inert a Grignard decomposition reaction forms a soluble atmosphere glove box continuously purged with high purity N z (<5ppm) generated using a N z generator (Spantech, model NG 300-1, UK) or under a positive * NCL communicationno. 5702 pressure of high purity N 2 using standard bench-top inert t To whom correspondence should be addressed atmosphere techniques. 0032-3861/94/06/1287-04 ~) 1994 Butterworth-HeinemannLtd POLYMER Volume 35 Number 6 1994 1287 Study of a soluble Mg-Ti catalyst." G. Satyanarayana and S. Sivaram Synthesis of MgCl 2.2THF RESULTS AND DISCUSSION A three-necked round-bottom flask equipped with a Preparation of MgCI2.2THF magnetic bar, N2 inlet, addition funnel and a reflux The THF adduct of MgC12 was prepared by a condenser was flame dried and cooled under NE single-step decomposition of Grignard reagent derived atmosphere. Iodine activated Mg turnings were placed from Mg metal and 1,2-dichloroethane in THF at 60°C: in the flask and THF was added at 40°C. 1,2-Dichloro- ethane (30ml) was added dropwise to the refluxing THF,60°C THF until all the Mg turnings dissolved. Evolution of Mg + CI-CH2-CH2-C1 ~ MgC12.2THF + C2H 4 ethylene indicating rapid decomposition of fl-chloroethyl- The solid complex precipitated out of solution. Although magnesium chloride and concomitant formation of a the facile decomposition of a Grignard reagent derived THF complex of MgCI z was observed. The solid was from Mg metal and 1,2-bromoethane is reported in the filtered and dried under vacuum for 8 h at 30°C (yield literature 13, the analogous reaction with 1,2-dichloro- 16.5g; Mg= 10.5%, C1=27.8%). ethane appears to have no precedent. Complexes of Preparation of soluble catalyst MgC12 with THF have been synthesized earlier by MgCIz.2THF (2g) was placed in a three-necked Handlir et al. 14 by the reaction of HgC12 and Mg metal round-bottom flask fitted with a condenser, N z inlet and in THF at 60°C. The complex isolated was observed to a septum. Xylene (50 ml) was added in the flask followed be insoluble in hexane or xylene even at refluxing by TNB (4 ml) using a hypodermic syringe. The slurry temperatures. was heated at 60°C in an oil bath for 8 h with stirring. Elemental analysis established the stoichiometry of the It was found that the solid slowly dissolved in the xylene complex as MgC12.2THF. The presence of THF was phase. The reaction mixture was cooled. The unreacted established by the appearance of triplets at 3.7 and MgClz.2THF was allowed to settle and the supernatant 5.7 ppm in the 1H n.m.r, spectrum in D20 as solvent and bands at 1039 and 885 cm- t in the FTl.r. spectrum. The clear liquid was transferred by a cannula into an Aldrich Sure/Seal ® bottle under N z pressure. The clear liquid powder XRD spectrum of MgC12.2THF showed strong was analysed for Ti (8.7 mg) and Mg (3.8 mg) in 1 ml of reflections at 20=29.2, 32.4 and 40.8° . In comparison, xylene solution. anhydrous MgC12 (Toho Titanium Co., Tokyo, Japan) showed all the above reflections and also a noticeable Polymerization of ethylene reflection at 20=31.5 ° which is absent in MgCI2.2THF. Polymerization was performed in a stirred glass cell at The powder XRD pattern of MgC12. 2THF is in agreement 1 atm (1 × l0 s Pa) of ethylene in xylene and hexane as with that reported in the literature but prepared by a diluents. A gas burette with a reservoir containing silicone different route ~4. The results show that the complex is oil was used to feed ethylene continuously to the cell. highly crystalline. The complex had a total pore surface The reaction cell was dried at 120°C overnight and cooled area of 10 m 2 g- 1 and a mean pore volume of 0.83 cm 3 g - 1. under N2. Solvent was introduced into the cell using a MgC12.2THF was subjected to t.g.a. (N2 atmosphere, hypodermic syringe followed by xylene soluble Mg-Ti 50-300°C, rate of 10°C min-1). The results showed that catalyst (0.2 ml) with a hypodermic syringe. The solvent the THF loss occurred in a two-stage process. The total was saturated with ethylene. Polymerization was initiated weight loss was observed to be 74% which corresponds by the addition of an organoaluminium compound. The to 2 mol of THF per mole of MgCI2 (Figure 1). reaction temperature was maintained by circulating water from a thermostat through the jacket of the cell Preparation of soluble Mg-Ti catalyst and the gas burette. Ethylene uptake was measured as a Under defined experimental conditions, MgCIz.2THF function of time. The reaction was terminated after 30 rain and TNB were found to be soluble in xylene at 60°C by addition of acidified methanol. The polymer was forming a homogeneous solution. The solution typically filtered and dried at 40°C under vacuum. analysed for Ti and Mg, 8.7 and 3.8 mg ml- 1, respectively. However, upon addition of hexane a solid precipitated Analysis out which, after repeated washing with dry hexane, Chlorine and magnesium estimation was performed by argentimetric and EDTA titrations, respectively. The Ti content in the catalyst was determined by the u.v. technique using a Hitachi (model 220) u.v.-visible spectro- 100 photometer lz. The n.m.r, spectrum of the support was recorded in D20 using a Briiker FT-80n.m.r. spectro- meter. The Fourier transform infra-red (FTi.r.) spectrum 75 of support was run on a Perkin-Elmer 16PC FT-IR in Nujol mull using NaCI cells (1600--400 cm-1). The E: powder X-ray diffraction (XRD) was recorded on a D3 50 Phillips PW 1730 spectrometer using Ni-filtered CuK~ o radiation.